Taxonomic systems are used not only to indicate relationships among organisms, but also to help identify organisms, whether we wish to do so purely for pleasure or for research purposes. Taxonomists publish written descriptions of species being characterized and named for the first time. In addition, a description of a group of organisms is usually accompanied by a taxonomic key, which taxonomists design to help identify specimens belonging to the group in question. One of the most useful forms of key is dichotomous: At each step, species are divided into two groups on the basis of the presence, absence, or degree of development of some characters. As an example, consider the key in the Figure for the identification of insects belonging to the order Odonata. This simple key allows identification only to the family level. Other keys must be used to identify species. Note that the characters chosen for use in the key are simple and easy to see. They are not necessarily the characters that reveal the most about evolutionary relationships among dragonflies and damselflies.It is not necessary to know anything about evolutionary relationships within a group to make a useful taxonomic key. All you need are characters that clearly separate the organisms and that can be used on most specimens. For example, it is often important to be able to identify plants that are not in flower. To do so requires the use of keys based on leaf and stem features. However, evolutionary relationships among plants are revealed much more clearly by their reproductive structures (flowers) because those structures evolve more slowly than leaves and stems do.